Junkers EF 110

The EF 110 was proposed by Junkers as a ‘Schnellstbomber’ (engl. fast bomber). The EF 110 featured a single fuselage design housing a powerful DB 613 engine, essentially twin DB 603s merged, propelling contra-rotating props at its nose. This configuration resulted in an exceptionally broad fuselage, accommodating two 500 kg bombs side by side within its internal bomb bay. The sole schematic of the aircraft, is dated December 11, 1942. 

Paired DB engines were a common way to boost power output of a single nacelle without the need to embark on a costly new engine development. In reality however, the installation of double engines turned out to be more complex than anticipated after all. An example of that was the He 177. The 177 was a twin nacelle multiple purpose aircraft. In essence a four engines bomber with two engines operating on a single propeller each. The design was plagued by continuous engine problems. 

There also was a single propeller, double engine Heinkel, the He 119.

Apparently Junkers engineers at least considered the option to build a fast bomber around a single DB 613. Only a single, minimalistic drawing survived [Luftwaffe, Secret Projects of the Third Reich', Dan Sharp]. A lot of the missing information has to be filled in from other sources: 

• Landing gear design
• Armament (type and location)
• Radiator
• Cockpit layout
• Engine exhaust

The available 3-view drawing is slightly enhanced and scaled. 

The side view vaguely highlights the location of the engine. From that, the location of the exhausts can be derived.  

Inspiration for the double engine exhaust system is taken from the He 177 bomber, where the two middle exhausts are channeled into a common ducted exhaust system.

The engine is crucial for the overall design. A good description of the DB 613 can be found here: [Source, external]

So the first efforts are dedicated to the CAD design of the engine, starting with a single DB 603. 

Cooling of piston engines is a major challenge since this requirement inevitably introduces drag. Commonly know is also the fact that the double DB installations suffered from severe cooling issues due to the nature of the asymmetric installation. Transporting heat out from in-between the engines proofed difficult, as experienced by the He 177 for instance. Similar issues would have to be expected for the EF 110. From the drawing, an oval shaped annular radiator seems to have been the choice. Again, similar to the He 177. The installation was also investigated and potentially planned for the 177, see image below. So the approach is also implemented in the CAD design of the 

Two internal 500 kg bombs are specified for the design. No other indications are made for additional armament in terms of cannons or guns. Complementary and as pure speculation, inspiration is drawn from DB613 installation studies conducted by Daimler Benz (see images below). Here, the central installation of a MK 412 cannon is proposed in different configurations. CAD studies confirm the feasibility, although the MK 214 was chosen instead. This is however purely speculative and not supported by sources. Similar to the MK 214 equipped Me 262, the EF 110 would have found itself in a bomber intercepting configuration. Subsequently, the bomb bay would serve as an additional fuel tank .

Some cannons need to fire through the prop arc and require synchronization. A similar issue was faced by the American XP-75. This would certainly reduce the rate of fire. Placing cannons with a decent amount of recoil far out in the wing inevitably creates large mending moments that would require structural reinforcements and hence increase the overall weight of the aircraft. 

Sources say nothing about armament (apart from the internal bomb bay). So, the following gun/ cannon arrangement is speculative. 

Most guns are outside the prop arc, apart from the two MG151's. The layout is inspired by FW studies for the Ta 152. A similar arrangement is chosen for the EF 110. It should be noted that the MG151 installation on top of the engine requires a slight change of the overall aircraft profile. Similar to the Ta 152, two bulges are introduced to accommodate the armament. 

An internal bomb bay accommodating two 500 kg bombs is also part of the design.The location of the bomb bay seems to be located well behind the CG. This would create a down pitching moment upon bomb release. How this was accounted for is uncertain. But I have chosen to keep this in accordance with the original drawings.